1. Field of the Invention
The invention relates in general to an illumination device. More particularly, this invention relates to an illumination device of a display.
2. Description of the Related Art
The conventional projection apparatus is basically applied to a front projection type or a large screen back projection type display. Light sources such as halogen lamps and arc lamps with enough luminance, for example, high pressure mercury lamp, metal halogen lamp, and xenon lamps, have to be used. These kinds of lamps have the advantage of high luminance, but also have the disadvantages such as high power consumption, short lifetime and high temperature. Therefore, these kinds of lamps are only used while a high luminance is required.
Referring to both FIG. 1A and FIG. 1B, two conventional illumination devices are shown schematically. FIG. 1A shows a projection apparatus disclosed in U.S. Pat. No. 5,418,583. A first lens array 20 and a second lens array integrator 30 are used to achieve the uniformity of a light source 10, followed by projecting the light onto a light valve 40. FIG. 1B shows another projection apparatus disclosed in U.S. Pat. Nos. 4,656,562 and 5,634,704. A light pipe integrator 25 and a lens 35 are used to uniformize a light source 10 and to project the uniform light onto a light valve 40. In Both FIGS. 1A and 1B, halogen lamps or various kinds of arc lamps have to be used to obtain the required luminance. Therefore, both of these two conventional projection apparatus have disadvantages such as high power consumption, short lifetime, abundant ultra-violet irradiation and high temperature. These conventional projection apparatus are thus not suitable for use in a display with a small feature size.
A desktop display normally has a diagonal length less than about 30 inches. Thus, the high luminance required by those large screens or display is not demanded for a desktop display. In addition, the desktop display is very often in an on status, so that a light source has to continuously provide a light for illumination. Again, those conventional illumination devices which use high pressure mercury lamp do not have enough lifetime are not suitable for use as a desktop display.
Apart from the high power consumption, short lifetime, and high temperature, the light source with a high luminance further has the disadvantages of hazard in application and high fabrication cost.